1. Field of the Invention
The present invention relates to a stainproof polyester fiber. More particularly, the present invention relates to a stainproof polyester fiber having an enhanced resistance to restaining while it is laundered or washed.
2. Description of the Related Arts
It is known that polyester fibers exhibit various excellent properties, for example, an excellent stability in dimension, a high mechanical strength, and a superior crease resistance, and therefore, are useful for various purposes.
However, it is also known that the polyester fibers are hydrophobic, and therefore, are easily stained with oil, which is difficult to remove, and are easily restained while being laundered or washed, in comparison with hydrophilic fibers, for example, cellulosic fibers.
This restaining phenomenon of the polyester fibers is an unsolved problem, known since the start of practical use of the polyester fibers in industry, and accordingly, various atempts have been made to eliminate the above-mentioned problem.
For example, Japanese Examined Patent Publication No. 47-2512 discloses a method for modifying a polyester fiber material by treating the polyester fiber material with an aqueous solution or dispersion of a copolymer of a polyoxyethyleneglycol with a polyester polymer, to enhance the hydrophilic property, stain proof property, and antistatic property thereof.
Japanese Examined Patent Publication No. 51-2559 discloses another method for modifying a synthetic fiber material by impregnating the synthetic fiber material with an aqueous solution of a hydrophilic vinyl monomer having a backbone segment consisting of a polyalkyleneoxide group and at least two terminal or side chain segments consisting of acrylate or methacrylate groups, and by polymerizing the hydrophilic vinyl monomer on the peripheral surfaces of the fibers in the synthetic fiber material at an elevated temperature, to enhance the hydrophilic property and antisatatic property of the synthetic fiber material.
Also, it is disclosed in Polymer, vol. 19, August, 1978, pages 908 to 912, that a polyester fiber material is treated by plasma initiated in various gases, for example, an oxygen-containing gas, to change the surface structure and wettability of the fiber material.
The above-mentioned known methods relate to finishing methods for modifying the polyester fiber material with a finishing agent. These known methods are disadvantageous in that the procedures are complicated, a specific apparatus is necessary, and reproductivity in effect is poor. Additionally, the known finishing methods are disadvantageous in that where the fiber materials are used in underwear or white clothes (e.g., hospital wear and uniforms) which are often laundered or washed, the finishing effect on the fiber material is gradually decreased with each repetition of the laundering or washing operation.
Accordingly, it is strongly desired to provide a new type of polyester fiber which has an excellent stainproof property durability and is not restained even when repeatedly laundered or washed.
Furthermore, it is known that the dyeability of polyester fibers can be improved by copolymerizing a polyester polymer with a polyoxyethyleneglycol. Thus, it was attempted to apply this idea to the improvement of the hydrophilic property and the stainproof property of the polyester fiber. As a result, it was found that, in order to obtain satisfactory levels of the hydrophilic property and the stainproof property, the polyoxyethyleneglycol must be copolymerized in a large amount of at least 10% by weight, preferably, at least 20% by weight, with the polyester polymer. This large amount of the copolymerized polyoxyethyleneglycol causes the resultant polyester copolymer fiber material to exhibit an unsatisfactorily decreased mechanical strength, an undesirably increased shrinkage in dimensions, and a deteriorated resistance to light. Therefore the resultant polyester copolymer fiber was useless for practical purposes, especially, for polyester fiber/cotton-blend fabrics which are used for linen articles. When the content of the copolymerized polyoxyethylene is reduced to 10% by weight or less, particularly 5% by weight or less, the resultant polyester copolymer fiber exhibited an unsatisfactory stainproof property.